Method for mould cooling in continuous casting

ABSTRACT

THIS IS A METHOD OF CONTROLLING THE COOLING OF A CONTINUOUS-CASTING MOULD IN WHICH A COOLANT SUCH AS WATER IS CIRCULATED THROUGH THE HOLLOW INTERIOR OF THE MOULD WALL FROM AN INLET AT THE BOTTOM TO AN OUTLET AT THE TOP. IN   ACCORDANCE WITH THIS METHOD A COUNTER-PRESSURE IS APPLIED TO THE COOLANT BY REGULATING THE OUT-FLOW.

March 23 1971 w. H-SUMM ERS Y 3,572,420

' METHOD FOR MOULD COOLING IN CONTINUOUS CASTING Filed Feb. 21, 1968 INVENTOR WILLIAM HENRY SWWRS I BY fwi/ guz ATTORNEYS United States Patent 3,572,420 METHOD FOR MOULD COOLING IN CONTINUOUS CASTING William H. Summers, Hampton Hall, near Malpas, England, assignor to Concast AG, Zurich, Switzerland Filed Feb. 21, 1968, Ser. No. 707,060

Claims priority, application Switzerland, Feb. 24, 1967,

2,846/ 67 Int. Cl. B22d 11/00 US. Cl. 16482 3 Claims ABSTRACT OF THE DISCLOSURE This is a method of controlling the cooling of a continuous-casting mould in which a coolant such as 'water is circulated through the hollow interior of the mould wall from an inlet at the bottom to an outlet at the top. In accordance with this method a counter-pressure is applied to the coolant by regulating the out-flow.

This invention relates to a method of cooling the mould during the process of continuously casting a metal, particularly steel, cooling being effected by a flowing medium.

The continuous casting of metals proceeds by pouring a melt into a cooled open-ended mould from which the casting, having formed a solidified crust containing a liquid core, is continuously withdrawn. The quality of the casting and its further processability depend decisively upon the quality of its surface. Frequent defects are cracks caused by a non-uniform and excessively abrupt cooling rate inside the mould.

One known method of reducing the liability of a casting to crack consists in reducing the intensity of the cooling effect by applying a coating of a material that is a poor conductor of heat to that side of the mould wall which is in contact with the coolant. However, this method has the drawback that once the coating has been applied the cooling conditions cannot be further varied, for instance in order to adapt them to different qualities of steel that are to be cast or to changes in the casting conditions themselves. Moreover, the application of such a coating presents certain difficulties.

It has also been proposed to provide the upper part of the mould with an insertion made of a material that is a poorer conductor of heat than that of the lower part of the mould, but the problem created by differential thermal expansion at the joints cannot as yet be considered as having been solved.

It is the object of the present invention to achieve a better cooling effect in the mould in order to prevent the creation of undesirable stresses and thus to improve the quality of the cast product.

According to the invention this problem is solved by submitting the coolant as it flows through the mould to counter-pressure generated and adjustable at the outlet end of the coolant from the mould. As referred to herein counter-pressure is the pressure applied in opposition to full flow as measured at the outlet valve which is provided to produce the desired amount of counterpressure. The amounts of counter-pressure specified herein are the amounts by which the pressure of fluid flowing through the outlet at full flow (suitably measured by a conventional gauge at the outlet) is increased by operating the outlet valve to restrict the outflow. By this means the intensity of the cooling effect can be mitigated and in desired regions kept uniform besides permitting the same to be controlled, and cast products that are substantially free from cracks can thus be produced. The counter-pressure modifies the conditions of flow in the cooling gap and by affecting the turbulance of the boundary layer which determines the transfer of heat the rate of abstraction of heat can be reduced. Moreover, the counterpressure applied to the coolant, such as water, also raises the pressure of the water inside the cooling gap and localized boiling which causes non-uniform cooling can be avoided. For instance, a counter-pressure of 11.38 p.s.i.g. raises the boiling point of Water from 99 C. to 116 C. Another advantage of the application of a counter-pressure is the greater uniformity of the resultant cooling effect by compensation of distortion of the mould wall. Moreover, the reduction of any gas-filled cavity, caused for instance by air bubbles, also has a favorable effect.

It has been established that the desired effect is optimal when the counter-pressure is between 4.27 and 42.66 p.s.i.g. depending upon existing conditions. When slabs are being cast the preferred pressure is between 7.11 and 21.33 p.s.i.g. When counter-pressure is applied a deaeratable mould may be used The counter-pressure may be generated in various ways. For instance, on the water outlet side a gate or like valve may be provided permitting the counter-pressure to be adjusted and controlled whilst casting proceeds. Regulation may be effected for instance by reference to the rate of abstraction of heat by the cooling Water.

For large slabs the longer side of the mould may be divided into several chambers and the counter-pressure separately controlled for each chamber as may be required.

An exemplary embodiment of apparatus adapted for applying the cooling method of this invention is illustrated in the accompanying drawing, which is a vertical section through a continuous-casting mould.

The mould 10 is an open-ended mould into the top end of which molten metal, such as steel, is poured. The mould, which is cooled by circulating water, or other suitable coolant, through a chamber 11 in the mould wall around the mould cavity, solidifies the periphery of the metal in the mould to form a continuous casting 12 having a solidified crust 13 and a liquid core 14. The casting 12 emerges from the bottom end of the mould. For cooling the mould 10 the coolant is fed through an inlet pipe 15 into the lower end of the chamber 11 and circulates up through the chamber 11 to the top end of the mould where it flows out through an outlet pipe 16. The circulation of coolant is preferably from the bottom to the top end of the mould. This provides the greatest cooling effect at the bottom end of the mould for forming and maintaining a sufficient thickness of solidified crust 13 to contain the liquid core 14 when the casting 12 emerges from the mould.

A gate valve 17, or other suitable fiuid flow adjusting valve, is provided in the outlet pipe 16 for applying and adjusting the counter-pressure applied to the coolant flowing through the mould chamber 11 in accordance with the method of this invention.

What I claim is:

1. The method of cooling a continuous-casting mould having means for circulating coolant through the mould wall under pressure from an inlet to an outlet comprising applying an adjustable counter-pressure at the outlet in which the counter-pressure is adjusted to be in the range of from about 4.27 to about 42.66 p.s.i.g.

2. The method of claim 1 in which the coolant is circulated from an inlet at the bottom end of the mould to an outlet at the top end.

3. The method of claim 2 in which the counter-pressure is in the range of from about 7.11 to about 42.66 p.s.1.g.

References Cited 4 3,293,692 12/ 1966 Rosenbaum 164-283X 3,321,008 5/1967 Jones 164283X FOREIGN PATENTS 35,476 2/1965 Germany 164283 706,817 4/1954 Great Britain. 164-283 U.S. Cl. X.R. 

